Optical detecting head

ABSTRACT

An optical detecting head for a line or edge target has a lighttight housing with a target-facing aperture in one end wall and a transverse wall portion intermediate its ends having a central opening therethrough; a target-illuminating optic fiber bundle extending through the central opening and having one end positioned within the target-facing aperture end divided into a plurality of target-illuminating optic fiber sub-bundles; a lamp socket supported on the opposite housing end wall; a light source lamp within the socket; a condenser lens between the lamp and the main target illuminating fiber bundle; and a diffuser plate between the lens and the lamp. The housing transverse wall portion has a plurality of light transmitting passages each of which receives a detector photocell. First and second pairs of receiver optic fiber bundles have ends within the target-facing aperture elongated in a direction parallel to the target and spaced equal distances on opposite sides of the target reference position and intermeshed with the target-illuminating fiber subbundles. Access holes through the housing wall register with the light transmitting passages, and light adjusting screws within the access holes protrude into the ligh transmitting passages and regulate the amount of light transmitted from the receiver fiber bundles to the individual detector photocells. A main feedback optic fiber bundle has one end facing the condenser lens and is divided at its opposite end into a plurality of feedback fiber sub-bundles each of which registers with one of the light transmitting passages. Light adjusting screws selectively block the amount of light transmitted from each feedback fiber subbundle to the associated detector photocell.

ilite State Vischulis Sept. 11, 1973 OPTICAL DETECTING HEAD alight-tight housing with a target-facing aperture in [76] mentor: Georgevischufis" W172 N9409 one elciid :all and a transverse wallpprtioiainterlrlnediate its en s aving a centra opening t eret roug atar- Shady Menomonee n get-illuminating opti c fiber bundle extendingthrough [22] Filed: Oct. 29, 1971 the central opening and having one endpositioned within the target-facing aperture end divided into a plu-[21] Appl' 193884 rality of target-illuminating optic fiber sub-bundles;a lamp socket supported on the opposite housing end Cl 50/ wall; a lightsource lamp within the socket; a condenser 3 /9 3 lens between the lampand the main target illuminating [51] Int. Cl. G02) 5/14 fiber bundle;and a diffuser plate between the lens and [58] Field of Search 350/96 B;250/227, the lamp, The housing transverse wall portion has a 250/237,219 D, 220, 202, 209, 204, 43.5, plurality of light transmittingpassages each of which 2 D 219 receives a detector photocell. First andsecond pairs of receiver optic fiber bundles have ends within the tar-[56] References Cited get-facing aperture elongated in a directionparallel to UNITED STATES PATENTS the target and spaced equal distanceson opposite sides 3,235,672 2/l966 Beguin 250 227 of the targetreference Positim and intermeshed with 3,340,764 9/1967 Bergwn 250/216the target-illuminating fiber sub-bundles. Access holes 3,198,949 8/1965Holdo 250/202 through the housing wall register with the light trans-3,636,362 l/l972 Beeman 250/227 mitting passages, and light adjustingscrews within the 167 1972 Hogue 6 access holes protrude into the lightransmitting pas- 3666,94l 1972 Watson 250/43-5 R sages and regulate theamount of light transmitted from 3,335,287 8/1967 Hargensm 250/202 thereceiver fiber bundles to the individual detector Hargens... photocens.A main feedback optic fiber bundle has one B end facing the condenserlens and is divided at its oppo- 3:430:057 2/1969 Genahr 350/96 B Siteend a Plurahty feedback fiber sub-hurdles Primary Examiner.lames W.Lawrence Assistant Examiner-D. C. Nelms Attorney-James E. Nilles [57]ABSTRACT An optical detecting head for a line or edge target has each ofwhich registers with one of the light transmitting passages. Lightadjusting screws selectively block the amount of light transmitted fromeach feedback fiber sub-bundle to the associated detector photocell.

38 Claims, 34 Drawing Figures PATENTEDSEPI 1 m 3.758.784

SHEEI 1 OF 8 FIG.1 F|G.2

PAIENIEII 3E? I I I973 3 7 58 7 84 SHEET 2 III 8 RECEIVER FIBERTERMINATION PATTERN F A TO PHOTO CELLS LIGHT FEEDBACK FIBERS RFC RFB I II I FIBER TERMINATION PATTERN AT PLANE FACING TARGET TARGET ILLUMINATIONFIBER TERMINATION PATTERN R,

. TARGEI' ILLUMINATION RELATIVE DIREcTIoN FIBERS OF CENTERLINE OF LINEOR EDGE TO BE DETECTED FIGS FIG.4

LIGHT SOURCE DIFFUSER AND HEAT ABS0RBER Ii :I"

CONDENSER LENS 45 F LIGHT FEEDBACK FIBERS PHOTOCELLS FIBERS CONDUCTINGLIGHT RFA To THE TARGET AREA LIGHT ADJUSTING MEANS RECEIVER FIBERS FIG.3 FIBER TERMINATION PLANE J SENSING PLANE TARGET RLANE sUREAcE f FLAT 0RCURVED PATENTEUSEPI I I975 3.758.784

sum 3 III a WIDTH OE DETECTOR OPERATIONAL FIELD A: VIEW AREA OI:PHOTOCELL PCA B= vIEw AREA OF PHOTOCELL PCB A C D B c: VIEW AREA OFPHOTOCELL PCC D= vIEw AREA OF PHOTOCELL PCD 41 WIDTH OI POSITIONDETECTION FIELD DIRECTION OF TARGET POSITION VARIATIONS TO BE DETECTEDF|G.6 V y W ACDB ACDB ACDB ACD'B IW/ //A LINE DARK LINE LIGHT EDGE EDGEBACKGROUND LIGHT BACKGROUND DARK DARK SIDE LEFT DARK SIDE RIGHT CONTRASTAB CD CONTRAST= AB CD CONTRAST A B CONTRAST= A B POSITION= C= DPOSITION: C D POSITION=AB=CD POSITION AB=CD FIG. 7A FIG. 75 FIG. 7C FIG.7D

ACDB Ac OB ACDB ACDB cONTRAsT= CONTRAST= CONTRAST= OONTRAST:

AB CD AB CD A B A B POSITION POSITION POSITION= POSITION:

C D c O AB CD AB CD FIG. 8A FIG.8B FIG.8C FIG.8D

ACDB ACDB CONTRAST: CONTRAST: CONTRAST: CONTRAST:

AB) CD AB CD A B -A B POSITION ROsITION= POSIT|ON= POSITION C D C(D ABCD AB CD FIG.9A FIGQB FIG.9C F|G.9D

PA'IENIED H97?- 3.758.784

sum 7 BF 8 co wo u mo n 40 ON Um 4N S m m a w a w w mo 40 m w n N om omma A x v am PATENTEU SEP! 1 I973 SHEET 8 (IF 8 AVG. OUTPUT LEVEL OF |l=|l AVG OUTPUT LEVEL OF 22=675 ADJUSTMENT OF FEEDBACK FIBER LIGHT ONLY I'5EFFECTIVE ILLUMINATION LEVEL ON PHOTOCELL Q I. 2 w w 0 L .L E E V 5 w ww w w v m .A L m L 1 r 0 l 5 O 0 5 ID 7. 5 6

A w S050 movwuzfiwmmu jwuoEoIu FIG. 23

2 0 3 W 0 U T U H I5 m 2 a m R T E 0 P w H F T i n W P R L N M A O Q OTwQ R E w w o N W D E m m M IIO N H L 2 l M U A 2 U J L D Cr L A w o n IL L E E W 2 5 N w E m T 5 L L. R w a w w H W L E L i n o m 5 u m o 5 h wSago me d wuz/Emmwu jwuoEoIu FIG.24

OPTICAL DETECTING HEAD This invention relates to apparatus for detectingthe position of a line or edge target such as may be formed by printedareas of different reflectivity and for deriving an electrical outputsignal which is a function of the deviation of the target from areference position.

BACKGROUND OF THE INVENTION Apparatus for monitoring an edge or linetarget formed by printed areas of different reflectivity is known, butsuch prior art detecting devices have not been entirely satisfactory.Should there be any change in the intensity of the light received by adetector photocell other than that resulting from deviation of thetarget from the centerline reference position, the lateral position ofthe target will be adjusted by the control system in an effort tocorrect the light variation. After such movement, the position of thetarget will vary from the reference position and will be in error.

The outputs of detector photocells of known optical sensing heads arenot matched under identical conditions of target reflectivity. Theresponse versus illumination characteristic varies from cell to cellbecause of differences in area of photosensitive material anddifferences in transmissibility of protective coatings due tomanufacturing tolerances. Further, a certain amount of constant internalambient illumination finds its way to the detector photocells in varyingamounts because of fixed reflecting surfaces common to both thetransmitting and receiving optic fibers. Also the amount of lightreceived by the individual photocells may be different because theeffective transmission areas of the illuminating and receiving fibersvary due to manufacturing tolerances. The resulting unequal response ofthe detector photocells of known optical sensing heads may result inerroneous position-indicating output signals.

Known edge or line target position detectors do not adequatelycompensate for variations in light intensity encountered in useresulting from changes in in contrast, reflectivity or transmissibility,or width of the target. Known line or edge target sensing apparatus isincapable of monitoring a target in which wide variations inreflectivity occur or on which widely different patterns are printedbecause the resulting wide variances in gain, which are unrelated totarget position, cause instability of the closed loop control system.

The polarity of the output of known edge or line target positiondetecting devices changes when the orientation of the low reflectivityand high reflectivity por-' tions of the target reverse, and prior artposition detection apparatus required manual selection of outputpolarity when confronted with such target characteristic changes. Forexample, known edge or line target detecting devices require manuallyoperated means to switch the polarity of the output signal in order tochange from monitoring a left edge target to monitoring a right edgetarget, and consequently such apparatus is uncapable of monitoring acheckerboard pattern similar to that shown in FIG. 19.

Prior art position detecting apparatus cannot satisfactorily monitor anintermittent pattern similar to that illustrated in FIG. 20 and tends tomove the target laterally when intermittent spacing occurs in thetarget. Further, known position detecting devices require mechanicalswitch means to inactivate the apparatus when no target is present inorder to prevent erroneous position-indicating outputs.

SUMMARY OF THE INVENTION The present invention provides an improvedoptical detecting head for a line or edge target.

Another aspect of the invention is to provide an improved opticaldetecting head having a plurality of photocells monitoring a target inwhich all of the detector photocells respond in an identical manner to agiven level of illumination.

Still another aspect of the invention is to provide an improved opticaldetecting head having a plurality of photocells monitoring a target inwhich the active area of all of the detector photocells are exposed tothe same effective illumination.

Another object of the invention is to provide an improved opticaldetecting head having a plurality of photocells monitoring a target andmeans to compensate for unequal mounts of ambient light received by theindividual photocells.

Still another object of the invention is to provide an improved opticaldetecting head having a plurality of photocells monitoring a target andmeans for adjusting the amount of reflected light from the target thatis received by each of the detector photocells.

A still further object of the invention is to provide an improvedoptical detecting head having a plurality of photocells monitoring atarget and means for regulating the amplitude of the detector photocelloutput. Still another aspect is to provide such an improved opticaldetecting head having means to adjust both the amplitude and the levelof the detector photocell output.

A further object of the invention is to provide an improved opticalsensing head for a line or edge target position detector which obviatesthe above disadvantages of prior art apparatus and is fail-safe and canmonitor an intermittent target such as illustrated in FIG. 20 withouterroneous position-indicating outputs. Still another object is toprovide such an improved optical sensing head for a line or edge targetposition detector which can monitor a checkerboard pattern such asillustrated in FIG. 19 and does not require manual switching means tochange between monitoring a left edge and a right edge. A still furtherobject is to provide such an optical sensing head for a line or edgetarget position detector wherein the output always has the same polaritywhen the target is laterally displaced in a given direction from areference position regardless of whether the target is a line or a rightedge or a left edge and irrespective of the orientation of the lowreflectivity and high reflectivity portions of the target.

In accordance with the invention, a ligth-tight housing having atransverse wall portion intermediate its ends with a control openingtherethrough has a lamp socket supported within the housing adjacent onehousing end wall, a light source lamp mounted within the socket and inoptical alignment with a diffusor plate, a condenser lens, anda targetilluminating optic fiber bundle which faces the lens at one end andextends through the central opening and is divided at its opposite endinto a plurality of target illuminating fiber suband first and secondpairs of receiver optic fiber bundles have target-facing endsintermeshed with the target illuminating sub-bundles within the targetfacing aperture and are elongated in a direction parallel to the targetand are spaced equal distances on opposite sides of the target referenceposition so that they receive light reflected from discrete areas of thetarget, and at their opposite ends each receiver fiber bundle is alignedwith one of the light transmitting passages and thus registers with oneof the detector photocells. Adjusting screws protruding into the lighttransmitting passages selectively vary the amount of light passing fromeach receiver fiber bundle to the corresponding detector photocell. Amain feedback optic fiber bundle has one end facing the lens and extendsthrough the central opening and at its opposite end is divided into aplurality of feedback fiber sub-bundles each of which registers with oneof the light transmitting passages. Adjusting screws selectively varythe amount of light transmitted from each of the feedback fibersubbundles to the corresponding detector photocell.

These and other objects and advantages of the present invention willappear hereinafter as this disclosure progresses, reference being had tothe accompanying drawings.

GENERAL Reference may be had if deemed necessary or desirable toapplicants co-pending application Ser.- No. l93,822, filed Oct. 19, 1971which will issue as U.S. Pat. No. 3,718,82l on Feb. 27, 1973 and isentitled Automatic Adjusting Photoelectric Position Detector." Referencemay also be had if deemed necessary or desirable to applicantsco-pending application Ser. No. 193,8l6, filed Oct. 29, I971 for TargetPosition Detecting Device having Means to Adjust Response of Photocells.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical section viewthrough the scanning head of a preferred embodiment of the invention;

FIG. 2 is a vertical sectional view through the scanning head of FIG. 1,taken at right angles thereto;

FIG. 3 is a schematic view of the light paths in the scanning head ofFIG. 1;

FIG. 4 is a view taken along line 4--4 in FIG. 1 showing the terminationpattern of the illumination and receiver optic fibers at the planefacing. the target;

FIG. 5 is a view taken along line 5-5 in FIG. 1 showing the terminationpattern of the illumination and feedback optic fibers at the planefacing the condenser lens;

FIG. 6 schematically illustrates the areas viewed by the four detectorphotocells in the scanning head of FIG. 1;

FIGS. 7A, 7B, 7C and 7D show the areas viewed by the four detectorphotocells with a target centered at the reference position within theposition detection field when the target is respectively: (a) a dark(low reflectivity or transparant) line on a relatively light (highreflectivity) background; (b) a light (high reflectivity) line on arelatively dark (or transparant) background; (0) a right edge; and (d) aleft edge;

FIGS. 8A, 8B, 8C and 8D are views similar to FIGS. 7A, 7B, 7C and 7D,respectively, but with the target to the left of the centerlinereference position;

, FIGS. 9A, 9B, 9C and 9D are views similar to FIGS. 7A, 7B, 7C and 7D,respectively, but with the targetto the right of the centerlinereference position;

FIG. 10 is a schematic circuit diagram in block form of a preferredembodiment of the invention;

FIG. 11 is a logic table showing the polarity and condition of elementsof the circuit of FIG. 10 for each of the targets and target positionsrepresented in FIGS. 7A-7D, 8A-8D and 9A-9D;

FIG. 12 is schematic circuit diagram of a single photocell adjustingnetwork of the circuit of FIG. 10;

FIG. 13 is a schematic circuit diagram of the automatic gain controlshown in block form in FIG. 10;

FIGS. 14A and 14B are schematic circuit diagrams of power supplyswitches PSI-PS4 shown in block form in FIG. 10;

FIG. 15 is a schematic circuit diagram of the photocell signal summingnetwork AB and CD shown in block form in FIG. 10;

FIG. 16 is a schematic circuit diagram of the means I for maintainingthe light source lamp at a constant light output; I

FIG. 17 is a view taken along line 17-17 of FIG. 1; FIG. 18 is aschematic circuit diagram of the temperature control for the scanninghead shown in FIGS. 1 and2;

FIGS. 19 and 20 illustrate typical checkerboard and intermittent targetsrespectively;

FIGS. 21 and 22 schematically representelectrical network for anindividual photocell and the network for all four detector photocellsrespectively; and

. FIGS. 23 and 24 illustrate adjustment of the detector photocells byoptical means so that each is exposed to the same effective illuminationlevel.

DESCRIPTION OF A PREFERRED EMBODIMENT SCANNING I-IEAD The scanning headof the preferred embodiment of the invention shown in FIGS. 1 and 2detects the position-of a line or edge target such as formed by printedareas of different reflectivity'or by the edge of a longitudinallytransported web and includes a generally boxshaped body 40 .which may besupported by pairs of mounting studs 41 extending horizontally fromopposed sidewalls thereof. Body 40 has an upwardly facing square recess42 therein which encloses a condenser lens 45 and the upper end of atubular optics conduit 46 havingits axis aligned with the optical axisof lens 45. A square light source base 47 having a central aperture 48therethrough is secured to body 40 by bolts 50 extending throughclearance holes in body 40. Light source base 47 has an annularhorizontal shoulder 51 around the margin of aperture 48 which supports aheat absorbing diffuser glass 53 above condenser lens 45. A cup-shapedlight source housing 59 shown in FIGS. 1, 2 and 5. Socket 58 is affixedto.

a U-shaped bracket 60 having flexible legs and portions 62 and 63extending horizontally from the legs thereof and being so. oriented thatthe elongated dimension of filament 59 is parallel to the referenceposition centerline as shown schematically in FIG. 5 and describedhereinafter. Portion 62 is affixed to the top wall 64 of light sourcehousing 56 by a screw 65 extending through top wall 64 and surrounded bya tubular spacer 67 disposed between the top wall 64 and portion 62. Thevertical position of horizontal portion 63 of bracket 60 may beselectively changed by a position adjusting screw 68 to move thefilament 59 of lamp LS from side to side in a direction transverse tothe reference position centerline and thus adjust the position of thelamp filament 59 relative to condenser lens 45. Lamp position adjustingscrew 68 extends through clearance holes in top wall 64 and inhorizontal portion 63 and is engaged by a nut beneath portion 63. Acompression spring 70 surrounding adjusting screw 68 urges horizontalportion 63 away from top wall 64. A depending lip 71 on portion 63engages the nut on adjusting screw 68 and prevents the nut from turning,and it will be apparent that turning of adusting screw 68 moveshorizontal portion 63 of bracket 60 toward or away from top wall 64 toadjust the position of lamp LS. Adjustment for major changes of filamentlocation from lamp to lamp are accomplished by lamp positioningadjusting screw 68.

A light reflector tube 75 surrounds lamp LS and fits within opening 48in light source base 47 above the head absorbing diffuser 53. Reflectortube 75 reflects light from filament 59 downward to the edges of dif--fuser 53 to provide relatively constant illumination across the detectoroperational field.

Condenser lens 45 is secured to a cup-shaped lens housing 74 which issupported by threaded vertical studs 76 (see FIG. 2) from the top wall64 of light source housing 56.

The square recess 42 in body 40 communicates with a horizontallyextending circular entrance opening 77 in body 40 which receives anelectrical cable. Body 40 also has a vertically extending cylindricalaperture 78 communicating with recess 42 which receives the tubularoptics conduit 46. The optics conduit 46 has a central opening ofgenerally rectangular cross section through which a bundle of targetilluminating optic fibers 79 extend for illuminating the target withlight from lamp LS. Bundle 79 preferably comprises a plurality of opticfibers which are suitably coated so that light is transmitted at highefficiency from one end of the bundle to the other.

A square optics plate 82 is secured to' the lower surface of body 40 bythe through bolts 50 and has a central aperture through which opticsconduit 46 protrudes. A cup-shape optics housing 84 having a centralopening 85 therethrough for the target illuminating optic fiber bundle79 is disposedbeneath optics plate 82. An optics block 87 which isgenerally T-shaped in cross section is disposed below optics housing 84,and cap screws 88 extend through clearance holes in optics block 87 andin optics housing 84 and in optics plate 82 and engage nuts (not shown)in optics plate 82 to support optics housing 84 and optics block 87 onbody 40.

Optics block 87 has a central square opening 90 therethrough whichreceives the bundle of target illuminating optic fibers 79 that transmitlight from lamp LS to illuminate e target. The termination pattern ofthe target illumination optic fibers 79 at the plane facing the targetas shown in FIG. 4, and it will be noted that the target illuminatingoptic fibers 79 are intermeshed with and disposed on both sides ofbundles of receiver optic fibers RF A, RFB, RFC and RFD which receivelight reflected from the target and transmit it to detector photocells.A protective glass lens 91 covers the ends of the optic fibers 79 whichilluminates the target and the light receiving ends -of the receiveroptic fiber bundles, and a lens retainer 92 affixed by screws to opticshousing 84 holds lens 91 in place.

A printed circuit board 94 is disposed within recess 42 in body 40 andhas a central opening surrounding optics conduit 46. Printed circuitboard 94 carries the four detector photocells PCA, PCB, FCC and PCD,

and a light source control photocell LSC, but only one photocell namelyphotocell LSC is shown in FIG. 1. The light paths through the opticfibers are shown schematically in FIG. 3. It will be noted that theoptic fibers of bundle 79 which extend through optics conduit 46illuminate the target, and individual bundles of receiver optic fibersRFA, RFB, RFC and RFD transmit light reflected from discrete areas ofthe target to the detector photocells PCA, PCB, PCC and PCD,respectively. Only a single bundle RFC of receiveroptic fibers isillustrated im -FIG. 1-, but it will be noted that receiver fiberbundles RFA, RFB, RFC and RFD extend through opening in optics block 87and through optics housing 84 and transmit the reflected light to theindividual detector photocells PCA, PCB, FCC and PCD. FIG. 4 illustratesthe termination pattern of the receiver fiber bundles RFA, RFB, RFC. andRFD at the plane facing the target. The reflected light receiving endsof the four receiver optic fiber bundles RFA, R-FB, RFC and RFD arespaced apart in a direction perpen: dicular to the reference positioncenterline at the position detector field, and the reflected lightreceiving ends of receiver optic fiber bundles RFA, RFB, RFC and RFD areintermeshed with target illuminating optic fibers so that targetilluminating optic fibers 79 are disposed on both sides of each receiveroptic fiber bundle at the plane facing the target as seen in FIG. 4.Further, the ends of the receiver fiber bundles RFA and RFB whichreceive the light reflected from the target and transmit it tophotocells PCA and PCB are disposed on opposite sides of the referenceposition centerline and outwardly from the ends of the receiver fiberbundles RFC and RFD which transmit light reflectedfrom the target tophotocells FCC and PCD. It will be appreciated that the optic fibers areshowngreatly enlarged in the drawing and that the target illuminationand receiver optic fiber bundles have a total cross sectionapproximately one-quarter inch by five-sixteenths inch at the planefacing the target.

The receiver fiber bundles RFA, RFB, RFC and RFD terminate at theirupper end within vertically extending apertures 101 (See FIG. 17) inoptics plate 82 which register with vertically extending lighttransmitting apertures 102 (see FIGS. 1 and 2) in body 40 in which thedetector photocells PCA, PCB, FCC and PCB and light source controlphotocell LSC on printed board 94 are mounted. Horizontally extendingapertures 104 in body 40 register with the vertical light transmittingapertures 102 in body 40 through which the light from the receiver fiberbundles RFA, RFB, RFC and RFD is transmitted to the detector photocellsPCA, PCB, FCC and PCB, and feedback light is transmitted tophotocellLSC. Nylon inserts 105 within apertures 104 have female threads thatengage light adjusting screws 106. The screws 106 can be turned manuallyto a position wherein they block a portion of the light transmitted fromone of the receiver fiber bundles RFA through RFD to the correspondingdetector photocell PCA, PCB, PCC or PCD.

Optics conduit 46 has a keyway slot 107 in which a bundle 109 offeedback optic fibers is disposed. At its upper end the feedback fiberbundle 109 receives light from condenser lens 45. Feedback bundle 109extends through keyway slot 107 and is divided into five feedback fiberbundles FFA, FFB, FFC, FFD and FFE. The four feedback fiber bundles FFA,FFB, FFC and FFD terminate within feedback fiber receiving apertures 111in optics plate 82 which register with the light transmitting apertures102 in body 40 through which the light from the receiver bundles RFA,RFB, RFC and RFD is transmitted to the detector photocells PCA, PCB, FCCand PCD. The feedback fiber bundle FFE also terminates within anaperture 111 in optics block 82 which registers with the lighttransmitting aperture 102 in body 40 in which the light source controlphoto'- cell LSC is disposed. Horizontal apertures 113 in optics plate82 register with vertical apertures 111,-and internally threaded nyloninserts 114 within horizontal apertures 113 engage light adjustingscrews 115 which may be manually turned to block a portion of the lightfrom the feedback fibers FF A, FFB, FFC and F FD received by photocells,PCA, PRB, PCC and PCD, respectively.

Condenser lens 45 and diffuser 53 provide uniform illumination acrossthe target illuminating fiber bundle 79 and across the feedback fiberbundle 109 so that the position of the filament 59 of lamp LS is notcritical. In-

embodiment provides an intense, uniform illumination asmuch as lampfilament 59 is elongated in a direction parallel to the referenceposition centerline and is longer in this direction than the bundles oftarget illuminating and feedback optic fibers as schematically shown inFIG.'5, all of the target illuminating and feedback optic fibers receivesubstantially uniform illumination in this direction. However, theposition of the filament 59 may vary from lamp to lamp in a directiontransverse to the reference position centerline, and lamp adjustingscrew 68 permits changing of the position of lamp filament 59 fromside-to-side along this dimension so that the optic fibers at theextreme limit of the detector operational field receives the same amountof light as the optic fibers of the center of the field. Thus turning oflamp adjusting screw 68 to move lamp filament 59 from side-to-side in adirection perpendicular to the reference position centerline permitsadjustment of the amount of light received by detector photocell Arelative to that received by detector photocell B, i.e., so that theportions of the target viewed by detector photocells A and B (which arefurther removed from the reference position) are illuminated equally bylamp LS.

I SCHEMATIC CIRCUIT DIAGRAM FIG. 10 is a functional diagram in blockform of a preferred embodiment of the automatic adjusting photoelectricposition detector of the invention disclosed and claimed in myco-pending application Ser. No.

bundles RFC and RFD, respectively). The preferred embodiment of theinvention is described as having reof the sensing field and closelycontrol the size, shape,

and location of the light-receptive areas of the photocells and alsofacilitates adjustment of photocells response characteristics asdescribed hereinafter.

FIGS. 7A, 7B, 7C and 7D show a target centered at the reference positionwithin the position detection field when the target is respectively: (a)a low reflectiv- .ity (or transparant) line on a relatively light (highreflectivity) background, (b) a high reflectivity line on a relativelydark (or transparant) background; (c) a right edge and (d) a left edge.The direction of target position deviation to be detected is shown inFIG. 6 and is perpendicular to the reference position centerlineillustrated in FIG. 4.

EDGE DETECTION MODE When the target is an edge, a two-positionmulti-pole selector switch 115 is manually actuated to the upper, orEDGE position as shown in FIG. 10. When the target is a line, the switch115 is manually actuated to the lower LINE position. The four detectorphotocells PCA, PCB, PCC and PCD are schematically shown in FIG. 10 asrectangles, designated A, B, C and D respectively, and this symbolrepresents both the corresponding photocell and the light adjustingcircuit therefor. The electrical adjusting circuit for each detectorphotocell PCA, PCB, PCC and PCD is the same and is shown in detail inFIG. 12 and discussed hereinafter. The outputs of the detectorphotocells PCA, PCB, PCC and PCD are respectively coupled to thenon-inverting input of power amplifiers 1, 2, 3 and 4 of the opera- Itional amplifier type and whose voltage gains are equal.

The outputs of power amplifiers 1 and 2 are coupled to the inputs of atwo-input photocell signal summing network, or averaging network ABshown in block'form which provides an output voltage that is thealgebraic average of its two input voltages and the circuit of j whichis shown in FIG. 15. The averaging network AB provides the output volageCD is the average C+Dl2 of the two input voltages C j and D from poweramplifiers 3 and 4 which amplify the output signal from the photocellsPCC and PCD, respectively. I

The output AB of averaging network AB at point 22 is coupled throughpole M53 of selector switch MS to the inverting input of an. outputpreamplifier 7 of the differential amplifier type and also to thenon-inverting input of an output preamplifier 8 of the differentialamplifier type. The output of the averaging network CD at point 23 iscoupled through pole M84 of selector switch MS to the non-invertinginput of output preamplifier 7 and also to the inverting input of outputpreamplifier 8.

The power supply to preamplifier 7 is controlled by voltage actuatedpower supply switches PS1 and PS2, and the power supply to preamplifier8 is controlled by similar voltage-actuated power supply switches PS3and PS4. The circuit diagrams of the voltage actuated power supplyswitches PS1 through PS4 are shown in FIGS. 14A and 14B.

Preamplifiers 7 and 8 share common signal sources (AB at point 22 and CDat point 23) for their inputs, but the signal sources are fed toopposite inputs of preamplifiers 7 and 8 so their outputs will benumerically equal in voltage but opposite in polarity. When the powersupply to preamplifiers 7 and 8 is cut off, these preamplifiers are inthe non-conductive condition and becomes passive circuit elements ofvery high impedance which effectively isolate their output terminalsfrom their input terminals. The output terminals of preamplifiers 7 and8 are commoned at point 24 and connected: (l) to the input of an outputpower amplifier 9; and (2) to the junction of two fail-safe leveladjusting resistances PR1 and PR2, one of which can be a potentiometer.The opposite ends of fail-safe resistances FRI and PR2 are connected tothe positive and negative terminals of the power supply, and it will beappreciated that the fail-safe resistances FRI and PR2 ground the input24 of output amplifier 9. Output power amplifier 9 amplifies the outputof either preamplifier 7 or 8 depending upon which one is active andsupplies the output signal of desired magnitude and polarity to suitablemeans (not shown) for returning the target to the reference positionwithin the position detector field. Such target positioning means mayneutralize at ground potential, but it will be appreciated that thefail-safe signal can be ground potential or any positive or negativevoltage selected.

The output of photocell PCA after being amplified in power amplifier lis coupled through pole MSl of selector switch MS to the inverting inputof a contrast differential amplifier and also to the non-inverting inputof a contrast differential amplifier 6. The output of photocell PCBafter being amplified by power amplifier 2 is coupled through pole M82of selector switch MS to the non-inverting input of differentialcontrast amplifier 5 and the inverting input of differential contrastamplifier 6. The input terminals of differential amplifiers 5 and 6 arethus connected to the common signal sources (signal A at point 11 andsignal B at point 12) in reverse to each other so that the output ofdifferential amplifier 5 is numerically equal to opposite in polarity tothe output of differential amplifier 6.

The output of contrast differential amplifier 5 at point i3 is coupledto the input of power supply switches PS2 and PS3, and the output ofdifferential amplifier 6 at point 14 is coupled to the input of powersupply switches PS1 and PS4. Power supply switches PSl through PS4 arevoltage-actuated transistorresistor logic, (TRL) switches whose circuitsare shown in FlGS. 14A and 14B and which control the availability of thepower supply to output preamplifiers 7 and 8. Power supply switch PS1only turns on to connect the positive power supply to preamplifier 7when the output of differential amplifier 6 at point 14 reaches apredetermined negative potential, e.g., 3.0 volts, and similarly powersupply switch PS2 only turns on to connect the negative power supply topreamplifier '7 when the output of differential amplifier 5 (at pointl3)reaches a predetermined positive potential, e.g., +3.0 volts. Powersupply switch PS 3 only turns on to connect the positive power supply tooutput preamplifier 8 when the output of differential amplifier 5 atpoint 13 reaches a predetermined negative potential, and similarly powersupply switch PS4 only turns on to connect the negative power supply tooutput preamplifier 8 when the output of differential amplifier 6 (atpoint 14) attains a predetermined positive potential, e.g., +3.0 volts.Consequently, if the outputs of differential amplifiers 5 and 6 are +3.0and -3.0 volts respectively, power supply switches PS1 and PS2 will bothbe on and preamplifier 7 will be active. Similarly, if the outputs ofdifferential amplifiers 5 and 6 are 3.0 and +3.0 volts respectively,power supply switches PS3 and PS4 will be turned on and preamplifier 8will be active. inasmuch as the outputs of contrast differentialamplifiers output relative to ground from power output amplifier 9 atpoint 25, and this is true regardless of whether the target is a line ora right edge or a left edge and irrespective of the orientation of thelow reflectivity and high reflectivity portions of the target. Stated inanother way, the output sense remains the same regard less of whetherthetarget is a left edge or aright edge or a line and irrespective ofthe polarity of contrast of the target.

When selector switch MS is in the EDGE position (edge detection mode),the contrast (target) polarity is determined by comparing signals A andB from photocells PCA and PCB. If the target is a right edge asillustrated in FIGS. 7C (edge centered), 8C (edge to left of center),and 9C (edge to right of center), photocell PCA receives less light thanphotocell PCB; A B; the output of differential amplifier 5 is positive;the output of differential amplifier 6 is negative; power switches PS1and PS2 are on so preamplifier 7 is active; and power switches PS3 andPS4 are off so preamplifier 8 is off. The magnitude of the detectoroutput signal from amplifier 9 at point 25 is determined by thenumerical difference of signals AB and CD, and the polarity of suchposition detector output signal from amplifier 9 is determined by therelative polarity of signals AB and CD and which of the preamplifiers 7or 8 is active. it will be appreciated that a signal such as AB becomesmore positive with increasing light to'the corresponding photocells.Still assuming that the target is a right edge, preamplifier 7 will beactive but the output of amplifier 9 will be zero when the edge iscentered as illustrated in FIG. 7C so that AB equals CD. Preamplifier 7will be active but the output of amplifier 9 will be positive when theright edge target is left of the reference position as shown in FIG. 8Cso that AB CD and the more positive signal CD is applied to thenon-inverting input of preamplifier 7. The polarity of the positiondetector output signal from amplifier 9 is negative when the right edgetarget deviates to the right of the reference position as shown in FIG.9C so that AB CD and the more positive signal is applied to theinverting input of preamplifier 7.The magnitude of the target positiondetector output signal from output amplifier 9 at point 25 is dependentupon the numerical difference of signals AB and CD.

Recalling that in the edge detection mode the contrast (target) polarityis determined by comparing signals A and B from photocells PCA and PCB,if the target is a left edge as shown in FIGS. 7D (edge centered), 8D(edge to left of center) and 9D (edge to right of center), photocell PCAreceives more light than photocell PCB; A B; the output of contrastdifferent amplifier 6 is positive and that of contrast differentialamplifier 5 is negative; power switches PS1 and PS2 are off sopreamplifier 7 is off, and power switches PS3 and PS4 are on sopreamplifier 8 is active. The polarity of the position detector outputsignal at point 25 is determined by the relative polarity of signals ABand CD. With the left edge target centered as shown in FIG. 7D, ABequals CD and the output from active preamplifier 8 is zero. With theleft edge target to the left of the reference position centerline asshown in FIG. 8D, AB CD and the output of amplifier 9 is positivebecause the more positive signal AB is coupled to the non-invertinginput of active preamplifier 8. With the left edge target to the rightof the reference position centerline as shown in FIG. 9D, AB CD and theoutput of amplifier 9 is negative because the more positive signal CD iscoupled to the inverting input of active output preamplifier 8.

As described hereinbefore, the power switches PS1 through PS4 do notturn on until the contrast is sufficiently great so that the outputs ofcontrast differential amplifiers 5 and 6 of the required polarity reacha predetermined magnitude. In other words, if the target contrast is toosmall for the detector to operate satisfactory, the contrast polarityswitches PS1 through PS4 will remain off and the output of amplifier 9will remain at a predetermined fail-safe value. Thus, when no validtarget is in the position detection field, the output signal from outputamplifier 9 does not change. The position detection apparatus thusreverts to a fail-safe output which may represent neutral, or inactionby the means (not shown) for positioning the target laterally.

Prior art position detectors cannot monitor intermittent patterns suchas shown in FIG. and tend to move the target laterally when anintermittent spacing occurs in the target. Such prior art positionsensing devices require mechanical switching means to inactivate theapparatus when no target is present in order to prevent false outputsand erroneous lateral movement of the target. Prior art positiondetection apparatus requires manually operated means to switch thepolarity of the output signal in order to change from monitoring a rightedge to monitoring a left edge, and consequently such prior art positiondetection apparatus cannot monitor the edges formed by the squares of acheckerboard pattern, such as illustrated in FIG. 19. The positiondetector disclosed herein atuomatically changes the contrast polarity atthe outputs of differential amplifiers 5 and 6 when changing betweenmonitoring a left edge and a right edge target and thus is capable ofautomatically monitoring a checkerboard pattern such means required byprior art apparatus.

LINE POSITION DETECTION Selector switch MS is manually actuated to thelower, or LINE position when the target is a line. In the LINE positionof selector switch MS, the output of averaging network CD is coupledthrough pole MSl to the inverting input of contrast differentialamplifier 5 and also to the non-inverting input of contrast differentialamplifier 6. Similarly, the output of averaging network AB is coupledthrough pole MS2 to the non-inverting input of differential amplifier 5and to the inverting input of differential amplifier 6. The output ofphotocell PCC after being amplified by power amplifier 3 is coupledthrough 'pole MS3 to the inverting input of preamplifier 7 and to thenon-inverting input of preamplifier 8. The output of photocell PCD afterbeing amplified in power amplifier 4 is coupled through pole MS4 to thenoninverting input of preamplifier 7 and to the inverting input ofpreamplifier 8.

Inthe line position detection mode, contrast (target) polarity isdetermined by comparing signals AB and CD, and the magnitude of theposition detection output 7 signal from the amplifier 9 atpoint 25 isdetermined by the numerical difference of the output signals fromphotocells PCC and PCD, as amplified by preamplifier 7 or 8, whicheveris active. The polarity of the target position signal at the output ofamplifier 9 is determined by the relative polarity of the signals fromphotocells PCC and PCD and which of the output preamplifiers 7 or 8 isactive.

Assume the target is a low reflectivity line against a relatively highreflectivity background as shown in FIGS. 7A (line centered), 8A (targetto left of center) and 9A (target to right of center). With thiscondition; AB CD; the input AB to the non-inverting inputto contrastdifferential amplifier 5 is greater than the signal CD to its invertinginput so the output thereof is positive; the output of contrastdifferential amplifier 6 is negative; contrast position switches PS1 andPS2 are on so that preamplifier 7 is active; and contrast positionswitches PS3 and PS4 are off so that preamplifier 8 is off. When theline target is centered as shown in F IG.

put signal from cell PCD', the magnitude of the position detector outputsignal appearing at the output of amplifier 9 is determined by thenumerical difference of signals C and D; and the output from amplifier 9at point 25 is positive since the signal D applied to the noninvertinginput of active preamplifier7 is greater than the signal C to itsinverting input. When the low reflectivity line target is to the rightof the reference position centerline as shown in FIG. 9A, the signalfrom photocell PCC the output signal from'photocell PCD; the positiondetector output signal appearing at the output from amplifier 9 at point25 is determined by the difference of signals C and D and .the polarityof this signal is negative since the input signal C to the invertinginput of active preamplifier 7 is greater than the input signal D to thenon-inverting input thereof.

If the target is a high reflectivity line against a relatively lowreflectively background as shown in FIGS. 73, 8B and 9B,.the lightreceived by photocells PCC and PCD is greater than the light received byphotocells PCA and PCB; signal AB signal CD; the output of contrastdifferential amplifier is negative since the signal CD to its invertinginput is greater than the signal AB applied to its non-inverting input;the output'of contrast differential amplifier 6 is positive; powersupply switches PSI and PS2 are off so that preamplifier 7 is off; andpower supply switches PS3 and PS4 are on so that preamplifier 8 isactive. If the line target is centered in the position detection fieldas shown in FIG. 78, equal amounts of light are received by photocellsPCC and PCD and the output of active preamplifier 8 and output amplifier9 is zero. If the high reflectivity line target is to the left of thereference position centerline as shown in FIG. 8B, the output signalfrom photocell PCC the output signal from photocell PCD so that thepolarity of the output from active preamplifier 8 and the positiondetector output signal appearing at the output of amplifier 9 ispositive. If the high reflectivity line target is to the right of thereference position centerline as shown in FIG. 9B, photocell PCDreceives more light than photocell PCC; signal C signal D, and thepolarity of the position detector output signal appearing at the outputof amplifier is negative.

The logic table of FIG. 11 summarizes all of the possible targetconditions illustrated in FIGS. 7, 8 and 9 and illustrates that theoutput sense" remains the same irrespective of whether the target is aline or a left edge or a right edge and also irrespective of thepolarity of contrast of such target. Stated in another manner, targetpositions to the right of the reference position centerline alwaysproduce a negative output with respect to ground from output amplifier 9at point 25, and target positions to the left of the reference positioncenterline always produce a positive output with respect to ground fromamplifier 9 at point 25.

AUTOMATIC GAIN CONTROL Targets of different contrast ratios (i.e., ratioof the lowest light reflectivity portion of the target to the portion ofhighest reflectivity) monitoredby known position detection devicesproduce responses of different magnitudes from the detector photocellsfor a given deviation of the target from the reference position. Suchdifferences in photocell response are independent of lateral deviationsof the target and therefore result in different detector outputs unlessmeans are provided to adjust the gain of the position detector. Manyknown position detection devices require manual adjustment of gain tocompensate for targets having different contrast ratios.

The position detector of the invention connects the sensing photocellsPCA, PCB, FCC and 'PCD in a closed loop amplifier control system whichcontinu-' ously and automatically adjusts the gain of the positiondetector to a constant value regardless of variations in contrast ratioof the target. This is accomplished by an automatic gain controlamplifier AGC shown in block' form in FIG. which provides a controlledpower supply to the light adjusting circuits for the detector photocellsPCA, PCB, PCC and PCD. The automatic gain control amplifier AGC ineffect decreases the voltage to all four detector photocells PCA, PCB,FCC and PCD when an increase in target contrast occurs thereby providinga constant target position-to-output relationship.

In the edge detection mode, the difference in the responses of thephotocells PCA and PCB which view areas of the target further removedfrom the reference position centerline is utilized as an indication ofcontrast in the target. The contrast logic signals from photocells PCAand PCB as amplified by power amplifiers 1 and 2, are inputs of thecontrast differential amplifiers 5 and 6; The outputs of differentialamplifiers 5 and 6 appearing at points 13 and 14 (which outputs areequal in magnitude but opposite in polarity) are coupled throughsimilarly poled steering diodes D1 and D2 to the input of the automaticgain amplifier AGC. Thesteering diode D1 or D2 to the input at point 15of automatic gain control amplifier AGC whose circuit is shown in FIG.13.

AUTOMATIC GAIN CONTROL AMPLIFIER AGC The output of contrast differentialamplifier 5 or 6 which is positive in polarity is coupled through thecorresponding steering diodes D1 or D2 to point 15 and through an inputresistor R1 to the base of a high gain amplifier NPN transistor Q1. Theseries arrangement of a capacitor C1 and a resistance R2 is connected inshunt to resistance R1 and forms a phase lead network which increasesthe gain of the Q1 stage when the contrast input of point 15 is rapidlychanging, thereby providing improvedhigh frequency response. Thecollector of transistor O1 is coupled through a resistance R5 to thepositive terminal of a DC power supply, and the emitter of transistor O1is connected through a resis tance R4 to the emitter of a PNP transistorQ2 whose collector is coupled tothe negative terminal of the powersupply. A resistor R3 connects the base of transistor O1 to the emitterof transistor 02. The resistances R1, R3, R4, and R5 determine the DCgain of the Q1 amplifier stage. The resistances R1 and R3 are selectedso that transistor 01 begins to conduct when an input signal ofapproximately 4.0 volts appears at point 15. The base of transistor Q2iscoupled to the junction of two resistances R7 and R6 forming a'voltagedivider between the negative terminal of the power supply and ground.Transistor Q2 and resistances R6 and R7 form a bias amplifier for the Q1stage to assure that the collector-of transistor Q1 can attain ground potential when transistor 01 is saturated. It will be appreciated thatincreases in the contrast inputsignal to amplifier AGC at point 15 willincrease the emitter current through transistor Q1 and the voltage dropacross collector resistor R5 and thus lower the voltage at the collectorof transistor Q1 and the positive and negative output voltages at points16 nd 17 respectively from amplifier AGC.

The collector of transistor O1 is connected to the base of a PNPtransistor Q3 having its emitter connected thpough a resistance R9 tothe positiveterminal of the power supply and itscollector coupledthrough a resistance R8 to the negative power supply terminal.Resistance R8 is equal to resistance R9, and the gain of the Q3 stage ispreferably equal to one. The emitter and collector of transistor Q areequal in voltage and of opposite polarity. The emitter of transistor O3is coupled through an emitter follower (current amplifier) transistor O4to the positive output terminal of amplifier AGC in FIGS. 12 and 22 eachof which comprises the serial arrangement of a photocell (such as PCA),a load resistance R14 and a trimming potentiometer R13. Resistances R14are chosen to match the resistance of the corresponding photocells at apredetermined level of illumination as described hereinafter. The outputof each photocell network A, B, C and D appearing at thejunction of thephotocell and its load resistance R14 is applied to the input of thecorresponding power amplifier 1, 2, 3 or 4.

As the positive input of amplifier AGC increases to a predeterminedlevel as a result of increase of contrast of the target, transistor Q1of the AGC amplifier is turned on, and amplifier AGC begins to decreasethe magnitudeof its positive and negative outputs at tenninals 16 and l'l-which'are the inputs to the photocell network A, B,-C and D for thephotocells PCA, PCB, PCC and PCD respectively. The outputs of thephotocell networks A, B, C, and D decrease in direct proportion to thedecrease'of the AGC amplifier outputs at points 16 and 17, and thereforethe inputsat points 11 and 12 to the. contrast differential amplifiers 5and 6 also decrease until equilibrium is reached between the AGCamplifier outputsat points 16 and 17 and the inputs to the contrastdifferential amplifiers at points 11 and 1 2. i

Since the gain of amplifier AGC is very high, only slight input signalchange at point 15 is required to realize the full output range ofamplifier AGC. Once the threshold of activation of amplifier AGC isattained by turning on transistor Q], the contrast signals at points 11and 12 are held virtually constant in magnitude. Inasmuch as thenetworks A, B, C and D for all four photocells PCA, PCB, PCC and PCDhave the same voltage source from terminals 16 and 17 of amplifier AGC,the response of all four photocells are attenuated equally, includingthose photocell signals resulting from change of target position.

The output amplitude capability of the photocells PCA, PCB, PCC and PCDis in direct proportion to the magnitude of the voltage supplied to themby amplifier AGC. Consequently, as the voltage supply to the photocellnetworks is varied, the output signals from the photocell networks willbe proportionally changed. The higher the contrast of the target, thelower the supply voltages to the photocell adjusting networks becomes.

Since contrast differential amplifier 5 or 6 in series with amplifierAGC has an extremely high loop gain, the output signals from thedetector photocells PCA, PCB, PCC and PCD approach a constant magnitudefor a given target position regardless of target contrast. Further,since the target contrast relates directly to the response of thedetector photocells, controlling the contrast signal magnitude to aconstant value correspondly controls the gain of the position detectorto a constant value. I

Pl-IOTOCELL MATCHING ADJUSTMENT Photocells PCA, PCB, PCC, PCD and LSCare preferably of the bulk-effect photoconductive type, al-

though the arrangement of the light reception areas with respect to atarget described hereinbefore is also operable with other types ofphotocells such as those of the photoemissive, photovoltaic, or thejunction photo conductive type.

The photocell circuits shown in FIGS. 12, 21 and 22, together with theoptical circuits schematically shown in FIG. 3 interconnecting the lightsource LS, the target and the detector photocells and the light sourcebrilliance control shown in FIG.' 16 together form a photocell matchingsystem which makes use of both light and electrical components to causethe four detector photocells PCA, PCB, PCC and PCD to respond in anidentical manner to identical illumination from the target as describedand claimed in my co-pending application Ser. No. 193,816 filed on evendate herewith. The biasing of the photocells through light feedbackfibers FF A through FFD accomplishes a response adjustment which isnotpossible by adjustment of electricalparameters only.

As described hereinbefore, the amount of light transmitted from lightsource LS to photocells PCA, PCB, PCC, PCD and LSC through thelight'feedback fibers FFA, FFB, FFC, F FD and FEE, respectively may beindividually adjusted bythe light adjusting screws and 106 (see FIG. 3)which may be manually turned to a position wherein each obstructs adesired portion of the light transmitted from the corresponding feedbackfiber bundle FFA through FFE to the associated photocells PCA, PCB, PCC,PCD and LSC.

The response of bulk-type photoconductive cells to a given level ofillumination varies materially from' cell to-cell. The electricalresistance of such a photoconductive-cell of a given active materialexposed to a predetermined illumination level depends upon the physicalstructure of the active area, i.e., length and thickness'ofphotoconductive material and the area exposed to light. Further,even'assuming that bulk-type photoconductive cells of equal active areascould be selected,-variations in transmissibility of protective coatingsand windows from cell to cell make it virtually impossible tomanufacture photocells that are identical in response to a given levelof illumination. However, bulk-type photoconductive cells will exhibitresponse characteristics in precise proportion to each other when theeffective illumination on their active areas is the same. Consequently,calibration of the detector photocells PCA, PCB, PCC and PCD so thattheir outputs are matched under idential conditions of targetreflectivity requires adjustment of the effective illumination that eachphotocell receives under identical target conditions.

The resistances-R R R and R of the detector photocells PCA, PCB, PCC andPCD respectively may be different, but the photocells are connected inan electrical circuit schematically shown in FIG. '22 which (assumingthe'effective illumination of all four photocells is equal) will provideequal 'electrical output signals E E E and E since the response of eachphotocell will be in fact proportional to that of all the others. FIG.21 schematically represents the electrical circuit for an individualdetector photocell and is similar to FIG. 12 except that the photocellis represented by its resistance designated R and is shown connected inseries with a single load resistor R which is equal to the sum of thetrimming and load resistances R and R shown in FIG. 12.

lrior to mounting the detector photocells PCA, PCB, FCC and PCD in thescanning head, load resistors R R R and R are selected for theindividual photocells PCA, PCB, FCC and PCD in a calibrator so that eachload resistor precisely matches the resistance of the correspondingphotocell. The calibrator may vary illumination over a controlled rangeand indicate response of the cell for different load resistances so thatthe load resistance R for the cell under test may be selected bycomparison with a master photocell and its particular load resistor.

In the electrical circuit shown in FIG. 22, the resistance of each cell(such as R,,) and its load resistance (such as R form a voltage divideracross which is impressed the voltage E appearing at the output terminal16 and 17 of the automatic gain control amplifier AGC. (The potential Eequals the sum of the positive voltage +V with respect to groundappearing at terminal 16 and the negative voltage V appearing atterminal 17). The electrical output signal (such as E appears at thejunction of each photocell (such as R with its load resistor (such as RIn accordance with the laws of proportionality, all photocells so matedwith load resistances and exposed to identical effective illuminationwill be in the relation RLA/RA RLB/RB RLC/RC RLD/RD so their voltageoutputs will precisely match 04 on oc In a fiber optic system whereinthe light transmitting and light receiving optic fibers are in closeproximity to each other and reflecting surfaces such as glass lens 91are common to both the light illumination and receiving optic fibers,constant internal ambient illumination is transmitted to each detectorphotocell but the amount of such internal ambient illumination variesfrom cell to cell. Further, the effective transmitting area of theillumination fibers and optic fibers associated with each detectorphotocell may be different from that for the other cells due tomanufacturing tolerances. Consequently, the amount of light received byeach detector photocell may be considerably different from that receivedby the others even though the target is identical for all detectorphotocells.

The light adjusting screws 106 which regulate the amount of light thatthe detector photocells PCA PCD receive from the receiver optic fibersRFA RFD and the light adjusting screws 115 that regulate the amount oflight which the detector photocells PCA-PCD receive from the feedbackoptic fibers FF A-F FD comprise means for exposing each detectorphotocell PCA-PCD to the same effective illumination level. The lightadjusting screws 106 for the receiver optic fibers RFA-RFD control therange (A E or amplitude of the output signals E E as illustrated in FIG.24, where the adjustment screws 115 for the feedback optic fibers F FA-FFD control the average level of the output signals E E as illustratedin FIG. 23. Actually the two adjustments interact since raising thelight level received by the detector photocells PCA-PCD with thefeedback optic fiber adjustment screws 115 inherently reduces the range(change A5 of output signal or change AR of cell resistance for a givenchange of illumination level AL) since the cell now operates in a lowerAR area of the response curve as seen in FIG. 23. Also, increasing theamount of light received by the photocells by opening the receiver opticfiber adjustment screws 106 inherently lowers the average level of theoutput signals E E FIG. 23 illustrates the effective of turning only thefeedback fiber light adjusting screws 115 to increase the amount offeedback light received by the detector photocells PCA-PCD while theamount of feedback light is kept constant. The initial effectiveillumination level of the detector photocells is designated L theportion of the curve between points 1-1plots photocell resistance R (orelectrical output signal E against effective illumination level in therange L 5 to L +(AL 10), and it will be noted that the change in outputsignal AE for a given change in effective illumination level AL 10 isequal to 10 and further that the average output level signal E for theportion of the curve 1l has the magnitude of 1. The portion of the curvebetweenpoints 2-2 plots photocell resistance R, (or output signal Eversus effective illumination level when the feedback fiber lightadjusting screws 115 are opened to increase the initial illumination toL '10. The portion 2-2 of the curve covers the range of effectiveillumination levels from L 10 to L (AL l0), and it will be noted thatthe range, or change in output signal AE for the portion of the curve2-2 equals only 4.5 and that the average output level for the portion2---2 of the curve has the value 6.75. The complete curve shown in FIG.23 is the resultant E (or R versus effective cell illumination L forresistance R R has been chosen for each cell. Since the response of eachdetector photocell PCA-PCD with its matched load resistance R R must beon the resultant curve shown in FIG. 28, it will be appreciated that thetwo adjustments (i.e., feedback fiber light adjustment by screws andreceiver fiber light adjustment by screws 116) can cause all detectorphotocells to have identical responses to identical levels of targetreflectivity.

FIG. 24 illustrates the effect of turning the receiver fiber adjustingscrews 115 only to increase the amount of reflected light from thetarget transmitted to the detector photocells while the amount offeedback light is held constant. The portion 1--1 of the curve shows thevariation in photocell resistance R (or output signal E for an initialsetting L 5 of the receiver fiber adjusting screws 115 over the range L5 to L fl-(AL IO). The change AE in output signal over the illuminationrange AL, 10 is equal to- 10, and the average output signal level forthe portion of the curve l--1 has the value of 11. The portion 2-2 ofthe curve shows the photocell response when the receiver fiber adjustingscrews 115 are opened to double the amount of light received through thereceiver fibers to L 10 over the target illumination range L to L ,+(AL20). It will be noted that the'range, or change of output signal AEequals only 6.5 even though the change in illumination level AL; is alsodoubled, and further that the average output level is only 5.75 for theportion 2-2 of the curve. It will be appreciated that when the receiverfiber optic screw adjustment is changed, the initial illumination levelalso changes and has the same effect as the feedback fiber lightadjustment except that LIGHT SOURCE BRILLIANCE CONTROL The light sourcebrilliance control shown in FIG. 16 automatically maintains the lightsource lamp LS at a constant light output regardless of aging effectsand variation in ambient temperature, thereby keeping the detectorphotocells PCA, PCB, FCC and PCD in a desired range of illuminationlevels and permitting the photocell response characteristics to remainin precise adjustment at all times. The lamp LS is connected in serieswith the emitter-collector circuit of a power series transistor Q12across the terminals of a heavy duty DC power supply. Photocell LSCreceives'light from lamp LS through feedback fiber bundle FFE as shownin FIG. 3. The inverting input of an operational amplifier 30 of thelight source brillance control is connected through an input resistanceR24 to a voltage divider formed by two resistances R22 and R23 connectedin series between the positive terminal of a power supply and ground.The voltage divider formed by resistances R22 and R23 establishes the ibias for operational amplifier 30. Photocell LSC is connected in serieswith a resistance R21 between the positive terminal of the power supplyand ground and forms avoltage divider for active input to amplifier 30,and the voltage at the junction of photocell LSC and resistance R21 iscoupled through an input resistance R25 to the noninverting input ofamplifier 30. The output of operation amplifier 30 is coupled through avoltage regulating Zener diode Z11 to the base of a transistor Q11 whichis connected in a Darlington circuit with the power transistor Q12.Zener diode Z11 in series with a resistor R27 connected between the baseand the collector of transistor Q1 1 provides a load for amplifier 30,and the voltage drop across resistor R27 biases transistor Q11 on. Afeedback resistance R26 for amplifier 30 is connected between theemitter of transistor Q11 and the inverting input of amplifier 30 andestablishesthe gain of amplifier 30 as H A capacitor C11 connectedbetween the base of transistor Q11 and the inverting input of amplifier30 provides degenerative feedback and keeps the light source brillancecontrol stabilized.

TEMPERATURE CONTROL shown in FIGS. 1 and 2, so as to be in thermal heatexchange relation with body 40) is electrically connected in series witha resistance R32 across the Zener diode Z31. A PNP transistor 031 hasits emitter and base connected to opposite sides of thermistor RT andits collector coupled through a current limiting resistance R33 to thebase of a power transistor switch 032. The emitter of power transistorswitch Q32 is connected to the grounded negative terminal of the powersupply and its collector is connected to the positive terminal of thepower supply through a resistive heater element H (not shown in FIGS. 1and 2) which is mounted within recess 42 to be in thermal heat exchangerelation with body '40. Body40 thermally connects the heater element Hto the'thermistor RT and to the photocells PCA, PCB, PCC, PCD and LSC.Heater adds heat to body 40 so that it is maintained at a substantiallyconstant temperature above any ambient temperature that the positiondetection head may encounter in operation and any changes intemperatures of body 40 are detected by thermistor RT. The resultingchange in resistance of thermistor RT varies the potential across thebase-emitter junction of transistor Q31, and the consequent change incollector potential of transistor Q31 is coupled to the base of powertransistor switch.Q32 and varies the current through resistive heater Hin a direction to maintain body 40 at a substantially constanttemperature.

- What I claim is:

1. An optical detecting head for a line or edge target a main targetilluminating optic fiber bundle within said housing extending throughsaid opening in said transverse wall portion and having the targetfacing and divided into a plurality of target illuminating fibersub-bundles disposed within said target facing aperture,

a lamp socket supported .within said housing adjacent the opposite endwall thereof,

a lamp mounted within said socket,

a condenser lens,

means for supporting said lens within said housing between and inoptical alignment with said lamp and said main target illuminating fiberbundles,

a plurality of detector cells within said housing,

a plurality of receiver optic fiber bundles within said housing havingtarget-facing ends interleaved with said target illuminating fibersub-bundles within said target facing aperture,

means for supporting said detector photocells so that each registerswith one of said light transmitting apertures in said transverse wallportion,

means within said housing for supporting the opposite ends of saidreceiver fiber bundles in registry with individual ones of said lighttransmitting apertures and individual ones of said detector photocells,

the sidewall of said housing having a plurality of access openingstherein each of which is transverse to and communicates with one of saidlight transmitting passages, and

threaded light blocking means in each of said access openings accessiblefrom the exterior of said housing for selectively varying the amount oflight transmitted through said passage from the associated receiverfiber bundle to the corresponding detector photocell.

2. An optical detecting head in accordance with claim 1 wherein saidtransverse wall portion also has a plurality of receiver fiber bundlereceiving holes therein each of which registers with one of said lighttransmitting passages and accepts said opposite end of one of saidreceiver fiber bundles.

3. An optical detecting head in accordance with claim 1 wherein saidtarget illuminating sub-bundles are elongated in a direction parallel tosaid line or edge target and are spaced apart in a direction transverseto said target, and said target-facing end of each said receiver fiberbundle is elongated in a direction parallel to said target and hastarget illuminating fiber subbundles disposed on opposite sides thereof.

4. An optical detecting head in accordance with claim 3 wherein saidtarget is to be maintained at a reference position centerline and thetarget-facing ends of a first pair of said receiver fiber bundles withinsaid target facing aperture are spaced approximately equal distances onopposite sides of said centerline and the target-facing ends of a secondpair of said receiver fiber bundles within said target facing aperturesare spaced approximately equal distances on opposite sides of saidcenterline but outward from said first pair of receiver fiber bundles.

5. An optical detecting head in accordance with claim 3 wherein saidlamp has a filament elongated in a direction parallel to said target andincluding lamp adjusting means accessible from the exterior of saidhousing for selectively positioning said lamp socket so that saidfilament occupies any one of a plurality of progressively differentpositions in a direction transverse to said target.

6. An optical detecting head in accordance with claim 5 and including adiffusor plate, and means for supporting said diffusor plate within saidhousing between said lens and the lamp-facing end of said main targetilluminating fiber bundle.

7. An optical detecting head in accordance with claim 6 and including alight reflector tube disposed within said housing adjacent said diffusorplate and in surrounding relation to said lamp.

8. An optical detecting head in accordance with claim 1 wherein saidlens supporting means extends inward from the housing sidewall andengages the margin of said lens and blocks transmission of light fromsaid lamp to said main target illuminating fiber bundle except throughsaid lens.

9. An optical detecting head in accordance with claim l and including amain feedback optic fiber bundle within said housing extending throughsaid opening in said transverse wall portion and having one end facingsaid lens and at 'the opposite end having the optic fibers divided intoa plurality of feedback fiber subbundles, and including means forsupporting said feedback fiber sub-bundles so that each registers withone of said light transmitting passages and one of said photocells.

10. An optical detecting head in accordance with claim 9 wherein saidtransverse wall portion has a plurality of feedback bundles receivingholes therein each of which registers with one of said lighttransmitting passages and accepts one of said feedback fiber subbundles,and wherein said sidewall of said housing has a plurality of accessapertures therein each of which is transverse to and registers with oneof said feedback fiber receiving holes, and including threaded lightblocking means in each of said access apertures accessible from theexterior of said housing for selectively varying the amount of lighttransmitting through said feedback receiving hole from the associatedfeedback fiber sub-bundle to the corresponding detector photocell.

11. An optical detecting head in accordance with claim 10 wherein saidtransverse wall portion also has a plurality of receiver fiber bundlereceiving holes therein each of which registers with one of said lighttransmitting passages and accepts said opposite end of one of saidreceiver fiber bundles.

12. An optical detecting head in accordance with claim 11 whereinsaid'target illuminating sub-bundles are elongated in a directionparallel to said target and are spaced apart in a direction transverseto said target and said target-facing end of each said receiver fiberbundle is elongated in a direction parallel to said target and hastarget illuminating fiber sub-bundles disposed on both sides thereof.v

v 13. An optical detecting head in accordance with claim 12 andincluding a light source control photocell within said housing inregister with one of said light transmitting passages and wherein one ofsaid feedback fiber sub-bundles registers with said one lighttransmitting passage, and including means controlled by the output fromsaid light source control photocell for maintaining the voltage appliedto said lamp substantially constant.

4.. An optical detecting head in accordance with claim 12 whereinsaidlamp has a filament elongated in a direction parallel to said targetand including lamp adjusting means accessible from the exterior of saidhousing for selectively positioning said lamp socket so that saidfilament occupies anyone of a plurality of progressively differentpositions in a direction transverse to said target. a l

15. An optical detecting headin accordance with claim 14 wherein saidopening in said transverse wall extends longitudinally of .said housing,said light transmitting passages are arcuately spaced apart radiallyoutward from said main target illuminating bundle and also extendlongitudinally of said housing, and said access holes extend radiallyinward from the housing sidewall transverse to said light transmittingpassages.

16. An optical detecting head in accordance with claim 1 wherein saidhousing and said transverse wall portion are of metal and are in heatexchange relation with said detector photocells, and including electricheater means for heating said housing, and means including a thermistorwithin said housing for maintain ing the temperature of said housingsubstantially constam.

17. An optical detecting head for a line or edge target comprising, incombination, r a source lamp,

a condenser lens adjacent said source lamp,

a main target optic fiber'bundle having one end in alignment with theaxis of said lens and at the end facing the target having the opticfibers divided into a plurality of sub-bundles spaced apart in a di-

1. An optical detecting head for a line or edge target comprising, incombination, a light-tight hollow housing having a target-facingaperture in one end wall to be positioned opposite said target and alsohaving intermediate its ends a wall portion transverse to the housingsidewall with an opening therethrough and a plurality of lighttransmitting passages therein , a main target illuminating optic fiberbundle within said housing extending through said opening in saidtransverse wall portion and having the target facing and divided into aplurality of target illuminating fiber sub-bundles disposed within saidtarget facing aperture, a lamp socket supporTed within said housingadjacent the opposite end wall thereof, a lamp mounted within saidsocket, a condenser lens, means for supporting said lens within saidhousing between and in optical alignment with said lamp and said maintarget illuminating fiber bundles, a plurality of detector cells withinsaid housing, a plurality of receiver optic fiber bundles within saidhousing having target-facing ends interleaved with said targetilluminating fiber sub-bundles within said target facing aperture, meansfor supporting said detector photocells so that each registers with oneof said light transmitting apertures in said transverse wall portion,means within said housing for supporting the opposite ends of saidreceiver fiber bundles in registry with individual ones of said lighttransmitting apertures and individual ones of said detector photocells,the sidewall of said housing having a plurality of access openingstherein each of which is transverse to and communicates with one of saidlight transmitting passages, and threaded light blocking means in eachof said access openings accessible from the exterior of said housing forselectively varying the amount of light transmitted through said passagefrom the associated receiver fiber bundle to the corresponding detectorphotocell.
 2. An optical detecting head in accordance with claim 1wherein said transverse wall portion also has a plurality of receiverfiber bundle receiving holes therein each of which registers with one ofsaid light transmitting passages and accepts said opposite end of one ofsaid receiver fiber bundles.
 3. An optical detecting head in accordancewith claim 1 wherein said target illuminating sub-bundles are elongatedin a direction parallel to said line or edge target and are spaced apartin a direction transverse to said target, and said target-facing end ofeach said receiver fiber bundle is elongated in a direction parallel tosaid target and has target illuminating fiber sub-bundles disposed onopposite sides thereof.
 4. An optical detecting head in accordance withclaim 3 wherein said target is to be maintained at a reference positioncenterline and the target-facing ends of a first pair of said receiverfiber bundles within said target facing aperture are spacedapproximately equal distances on opposite sides of said centerline andthe target-facing ends of a second pair of said receiver fiber bundleswithin said target facing apertures are spaced approximately equaldistances on opposite sides of said centerline but outward from saidfirst pair of receiver fiber bundles.
 5. An optical detecting head inaccordance with claim 3 wherein said lamp has a filament elongated in adirection parallel to said target and including lamp adjusting meansaccessible from the exterior of said housing for selectively positioningsaid lamp socket so that said filament occupies any one of a pluralityof progressively different positions in a direction transverse to saidtarget.
 6. An optical detecting head in accordance with claim 5 andincluding a diffusor plate, and means for supporting said diffusor platewithin said housing between said lens and the lamp-facing end of saidmain target illuminating fiber bundle.
 7. An optical detecting head inaccordance with claim 6 and including a light reflector tube disposedwithin said housing adjacent said diffusor plate and in surroundingrelation to said lamp.
 8. An optical detecting head in accordance withclaim 1 wherein said lens supporting means extends inward from thehousing sidewall and engages the margin of said lens and blockstransmission of light from said lamp to said main target illuminatingfiber bundle except through said lens.
 9. An optical detecting head inaccordance with claim 1 and including a main feedback optic fiber bundlewithin said housing extending through said opening in said transversewall portion and having one end facing said lens and at the opposite endhaving the optic fibErs divided into a plurality of feedback fibersub-bundles, and including means for supporting said feedback fibersub-bundles so that each registers with one of said light transmittingpassages and one of said photocells.
 10. An optical detecting head inaccordance with claim 9 wherein said transverse wall portion has aplurality of feedback bundles receiving holes therein each of whichregisters with one of said light transmitting passages and accepts oneof said feedback fiber sub-bundles, and wherein said sidewall of saidhousing has a plurality of access apertures therein each of which istransverse to and registers with one of said feedback fiber receivingholes, and including threaded light blocking means in each of saidaccess apertures accessible from the exterior of said housing forselectively varying the amount of light transmitting through saidfeedback receiving hole from the associated feedback fiber sub-bundle tothe corresponding detector photocell.
 11. An optical detecting head inaccordance with claim 10 wherein said transverse wall portion also has aplurality of receiver fiber bundle receiving holes therein each of whichregisters with one of said light transmitting passages and accepts saidopposite end of one of said receiver fiber bundles.
 12. An opticaldetecting head in accordance with claim 11 wherein said targetilluminating sub-bundles are elongated in a direction parallel to saidtarget and are spaced apart in a direction transverse to said target andsaid target-facing end of each said receiver fiber bundle is elongatedin a direction parallel to said target and has target illuminating fibersub-bundles disposed on both sides thereof.
 13. An optical detectinghead in accordance with claim 12 and including a light source controlphotocell within said housing in register with one of said lighttransmitting passages and wherein one of said feedback fiber sub-bundlesregisters with said one light transmitting passage, and including meanscontrolled by the output from said light source control photocell formaintaining the voltage applied to said lamp substantially constant. 14.An optical detecting head in accordance with claim 12 wherein said lamphas a filament elongated in a direction parallel to said target andincluding lamp adjusting means accessible from the exterior of saidhousing for selectively positioning said lamp socket so that saidfilament occupies any one of a plurality of progressively differentpositions in a direction transverse to said target.
 15. An opticaldetecting head in accordance with claim 14 wherein said opening in saidtransverse wall extends longitudinally of said housing, said lighttransmitting passages are arcuately spaced apart radially outward fromsaid main target illuminating bundle and also extend longitudinally ofsaid housing, and said access holes extend radially inward from thehousing sidewall transverse to said light transmitting passages.
 16. Anoptical detecting head in accordance with claim 1 wherein said housingand said transverse wall portion are of metal and are in heat exchangerelation with said detector photocells, and including electric heatermeans for heating said housing, and means including a thermistor withinsaid housing for maintaining the temperature of said housingsubstantially constant.
 17. An optical detecting head for a line or edgetarget comprising, in combination, a source lamp, a condenser lensadjacent said source lamp, a main target optic fiber bundle having oneend in alignment with the axis of said lens and at the end facing thetarget having the optic fibers divided into a plurality of sub-bundlesspaced apart in a direction transverse to said target and to thereference position center line for said target, four detectorphotocells, four bundles of receiver optic fibers for receiving lightreflected from discrete areas of said target, one end of each saidreceiver optic fiber bundle communicating with one of said detectorphotocElls and the end thereof facing said target being intermeshed withsaid target illuminating optic fiber sub-bundles, the target facing endsof one pair of said receiver fiber bundles being disposed equaldistances on opposite sides of said center-line and the target facingends of the other of said receiver fiber bundles also being disposedequal distances on opposite sides of said centerline but being furtherremoved from said centerline than said one pair, and adjustable meansdisposed between the photocell facing end of certain of said receiveroptic fiber bundles and the corresponding photocells for selectivelyobstrcting a portion of the light transmitted from said receiver fiberbundles to said photocells, each said light obstructing means includinga threaded light blocking member movable progressively to a plurality ofpositions between said photocell and said photocell-facing end of saidreceiver fiber bundle in which different amounts of light aretransmitted from said bundle to said photocell.
 18. An optical detectinghead in accordance with claim 17 and including means including a firstaveraging network for providing an output voltage which is the algebraicaverage of the outputs of the detector photocells which receive lightfrom said one pair of receiver fiber bundles, means including a secondaveraging network for providing an output voltage which is the algebraicaverage of the outputs of the detector photocells which receive lightfrom said other pair of receiver fiber bundles, and means for comparingthe output voltages from said first and second averaging network toderive a signal which is a function of target contrast or of targetposition when the target scanned by said detecting head is respectivelyon edge or a line.
 19. An optical detecting head in accordance withclaim 17 wherein said target-facing end of each of said receiver fiberbundles is elongated in a direction parallel to said centerline.
 20. Anoptical detecting head in accordance with claim 19 wherein said sourcelamp has a filament elongated in a direction parallel to said centerlineand including lamp adjusting means for selectively positioning said lampso that said filament occupies any one of a plurality of progressivelydifferent positions in a direction lateral of said centerline.
 21. Anopticl detecting head in accordance with claim 17 and including a mainfeeback optic fiber bundle having one end facing said condenser lens andat its opposite end having the optic fibers distributed into at leastfour optic fiber sub-bundles the ends of which face individual ones ofsaid detector photocells.
 22. An optical detecting head in accordancewith claim 21 and including means disposed between the photocell-facingend of certain of said feedback optic fiber sub-bundles and thecorresponding photocell for selectively blocking a portion of the lighttransmitted from said feedback fiber sub-bundle to said photocell. 23.An optical detecting head in accordance with claim 22 and including alight source control photocell, and wherein said feedback optic fiberbundle at said opposite end has the optic fibers divided into fivefeedback fiber sub-bundles the end of one of which faces said lightsource control photocell.
 24. An optical detecting head in accordancewith claim 23 and including means responsive to the output of said lightsource control photocell for maintaining the light intensity of saidsource lamp substantially constant.
 25. An optical detecting head inaccordance with claim 24 wherein said means for maintaining the lightintensity of said source lamp constant includes a power supply for saidsource lamp and means responsive to the output of said light sourcecontrol photocell for maintaining the voltage of said power supplysubstantially constant.
 26. An optical detecting head for either a lineor an edge target comprising, in combination, a source lamp, a condenserlens facing said lamp, a main target illuminating optic fiBer bundlecoaxial with said condenser lens to receive illumination from said lampand at the end facing the target having the optic fibers divided into aplurality of sub-bundles spaced apart in a direction transverse to saidtarget and to the reference position centerline for said target, fourdetector photocells, four bundles of receiver optic fibers for receivinglight reflected from discrete areas of said target, one end of each ofsaid receiver optic fiber bundles communicating with one of saiddetector photocells and the target-facing ends of said receiver opticfiber bundles being disposed between said target illuminating opticfiber sub-bundles, the target-facing ends of one pair of said receiverfiber bundles being disposed approximately equal distances on oppositesides of said centerline and the target-facing ends of a second pair ofsaid receiver fiber bundles also being disposed approximately equaldistances on opposite sides of said centerline and spaced outwardly fromsaid target-facing ends of said one pair, adjustable means disposedbetween the photocell-facing end of certain of said receiver optic fiberbundles and the corresponding photocell for selectively varying theamount of light transmitted therebetween, a main feedback optic fiberbundle having one end facing said condenser lens to receive light fromsaid lamp and at its opposite end having the optic fibers divided intoat least four feedback fiber out-bundles each of which has one endfacing one of said detector photocells, and adjustable means disposedbetween the photocell-facing end of certain of said feedback optic fibersub-bundles and the corresponding photocell for selectively varying theamount of light transmitted from said feedback optic fiber sub-bundle tosaid photocell.
 27. An optical detecting head in accordance with claim26 and including means including a first averaging network for providingan output voltage which is the algebraic average of the outputs of thedetector photocells which receives light from said one pair of receiverfiber bundles, means including a second averaging network for providingan output voltage which is the algebraic average of the detectorphotocells which receive light from said second pair of receiver fiberbundles, and means for comparing the output voltages from said first andsecond averaging networks to derive a signal which is a function oftarget contrast or of target position when the target scanned by saiddetecting head is respectively an edge or a line.
 28. An opticaldetecting head in accordance with claim 26 wherein said target-facingends of said receiver fiber bundles are elongated in a directionparallel to said centerline and to said target.
 29. An optical detectinghead in accordance with claim 26 wherein said means for selectivelyvarying the amount of light transmitted between a fiber bundle orsub-bundles and a photocell includes a threaded light blocking membermovable progressively to a plurality of positions between said bundle orsub-bundle and said cell in which different amounts of light aretransmitted therebetween.
 30. An optical detecting head in accordancewith claim 26 having a hollow housing provided intermediate its endswith a wall portion transverse to the housing sidewalls, said housingenclosing said lamp and said lens and said transverse wall portionhaving an opening therethrough in alignment with the axis of said lensthrough which said main target illuminating optic fiber bundle extendswithin said housing and also having at least four light transmittingpassages arcuately spaced apart radially outward from said opening, andmeans for supporting said detector photocells within said housing sothat each registers with one of said light transmitting passages.
 31. Anoptical detecting head in accordance with claim 30 wherein said hollowhousing is light-tight and encloses said receiver fiber bundles and hasa target-facing aperture in one end wall into which saIdtarget-illuminating sub-bundles and the target-facing end of saidreceiver fiber bundles extend, and including means within said housingfor holding the photocell-facing end of each of said receiver fiberbundles in register with one of said light transmitting passages.
 32. Anoptical detecting head in accordance with claim 31 wherein said mainfeedback optic fiber bundle is within said housing and extends throughsaid opening in said transverse wall portion, and including means withinsaid housing for holding one end of each of said feedback optic fibersub-bundles in register with one of said light transmitting passages.33. An optical detecting head in accordance with claim 32 wherein thesidewall of said housing has a plurality of peripherally spaced accessopenings therethrough each of which is transverse to and registers withone of said light transmitting passages and is accessible from theexterior of said housing, and wherein said adjustable means forselectively varying the amount of light transmitted from said feedbackoptic fiber sub-bundles includes adjustable threaded light obstructingmeans in each of said access openings for selectively varying the amountof light passing through said light transmitting apertures to thecorresponding detector photocell.
 34. An optical detecting head inaccordance with claim 33 wherein said transverse wall portion has atleast n feedback fiber receiving holes each of which registers with oneof said light transmitting passages and receives the photocell-facingend of one of said feedback optic fiber sub-bundles and said feedbackfiber receiving holes constitute said means for holding said feedbackfiber sub-bundles in register with said light transmitting passages, andwherein the sidewall of said housing has a plurality of peripherallyspaced access apertures each of which is transverse to and registerswith one of said feedback fiber receiving holes and including adjustablethreaded light obstructing means in each of said access passages forselectively varying the amount of light transmitted from the feedbackoptic-fiber sub-bundle received with said hole to the correspondingdetector photocell.
 35. An optical detecting head in accordance withclaim 32 wherein said transverse wall portion has five lighttransmitting passages therein and including a lamp source controlphotocell and wherein said means for supporting said detector photocellsalso supports said lamp source control photocell so that it registerswith one of said light transmitting passages.
 36. An optical detectinghead in accordance with claim 32 wherein said opposite end of said mainfeedback optic fiber bundle is divided into five feedback optic fibersub-bundles and said means for holding said feedback optic fibersub-bundles also holds one of said feedback optic fiber sub-bundles inregister with said light transmitting passage which communicates withsaid light source control photocell.
 37. An optical detecting head inaccordance with claim 34 wherein said target-facing ends of saidreceiver fiber bundles are interleaved with said target illuminatingfiber sub-bundles and said target-facing ends of said receiver fiberbundle and said target illuminating sub-bundles are elongated in adirection parallel to said centerline and to said target.
 38. An opticaldetecting head in accordance with claim 37 and including a lamp socketmounted within said housing releasably receiving said source lamp, adiffusor plate within said housing between said lens and said sourcelamp, and wherein said lamp has a filament elongated in a directionparallel to said centerline, and including lamp adjusting meansaccessible from the exterior of said housing for selectively positioningsaid lamp socket so that said lamp filament occupies any one of aplurality of progressively different positions in a direction laterallyof said centerline.